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impl.py
# sqlalchemy/pool.py # Copyright (C) 2005-2021 the SQLAlchemy authors and contributors # <see AUTHORS file> # # This module is part of SQLAlchemy and is released under # the MIT License: http://www.opensource.org/licenses/mit-license.php """Pool implementation classes. """ import traceback import weakref from .base import _ConnectionFairy from .base import _ConnectionRecord from .base import Pool from .. import exc from .. import util from ..util import chop_traceback from ..util import queue as sqla_queue from ..util import threading class QueuePool(Pool): """A :class:`_pool.Pool` that imposes a limit on the number of open connections. :class:`.QueuePool` is the default pooling implementation used for all :class:`_engine.Engine` objects, unless the SQLite dialect is in use. """ def __init__( self, creator, pool_size=5, max_overflow=10, timeout=30, use_lifo=False, **kw ): r""" Construct a QueuePool. :param creator: a callable function that returns a DB-API connection object, same as that of :paramref:`_pool.Pool.creator`. :param pool_size: The size of the pool to be maintained, defaults to 5. This is the largest number of connections that will be kept persistently in the pool. Note that the pool begins with no connections; once this number of connections is requested, that number of connections will remain. ``pool_size`` can be set to 0 to indicate no size limit; to disable pooling, use a :class:`~sqlalchemy.pool.NullPool` instead. :param max_overflow: The maximum overflow size of the pool. When the number of checked-out connections reaches the size set in pool_size, additional connections will be returned up to this limit. When those additional connections are returned to the pool, they are disconnected and discarded. It follows then that the total number of simultaneous connections the pool will allow is pool_size + `max_overflow`, and the total number of "sleeping" connections the pool will allow is pool_size. `max_overflow` can be set to -1 to indicate no overflow limit; no limit will be placed on the total number of concurrent connections. Defaults to 10. :param timeout: The number of seconds to wait before giving up on returning a connection. Defaults to 30. :param use_lifo: use LIFO (last-in-first-out) when retrieving connections instead of FIFO (first-in-first-out). Using LIFO, a server-side timeout scheme can reduce the number of connections used during non-peak periods of use. When planning for server-side timeouts, ensure that a recycle or pre-ping strategy is in use to gracefully handle stale connections. .. versionadded:: 1.3 .. seealso:: :ref:`pool_use_lifo` :ref:`pool_disconnects` :param \**kw: Other keyword arguments including :paramref:`_pool.Pool.recycle`, :paramref:`_pool.Pool.echo`, :paramref:`_pool.Pool.reset_on_return` and others are passed to the :class:`_pool.Pool` constructor. """ Pool.__init__(self, creator, **kw) self._pool = sqla_queue.Queue(pool_size, use_lifo=use_lifo) self._overflow = 0 - pool_size self._max_overflow = max_overflow self._timeout = timeout self._overflow_lock = threading.Lock() def _do_return_conn(self, conn): try: self._pool.put(conn, False) except sqla_queue.Full: try: conn.close() finally: self._dec_overflow() def _do_get(self): use_overflow = self._max_overflow > -1 try: wait = use_overflow and self._overflow >= self._max_overflow return self._pool.get(wait, self._timeout) except sqla_queue.Empty: # don't do things inside of "except Empty", because when we say # we timed out or can't connect and raise, Python 3 tells # people the real error is queue.Empty which it isn't. pass if use_overflow and self._overflow >= self._max_overflow: if not wait: return self._do_get() else: raise exc.TimeoutError( "QueuePool limit of size %d overflow %d reached, " "connection timed out, timeout %d" % (self.size(), self.overflow(), self._timeout), code="3o7r", ) if self._inc_overflow(): try: return self._create_connection() except: with util.safe_reraise(): self._dec_overflow() else: return self._do_get() def _inc_overflow(self): if self._max_overflow == -1: self._overflow += 1 return True with self._overflow_lock: if self._overflow < self._max_overflow: self._overflow += 1 return True else: return False def _dec_overflow(self): if self._max_overflow == -1: self._overflow -= 1 return True with self._overflow_lock: self._overflow -= 1 return True def recreate(self): self.logger.info("Pool recreating") return self.__class__( self._creator, pool_size=self._pool.maxsize, max_overflow=self._max_overflow, pre_ping=self._pre_ping, use_lifo=self._pool.use_lifo, timeout=self._timeout, recycle=self._recycle, echo=self.echo, logging_name=self._orig_logging_name, use_threadlocal=self._use_threadlocal, reset_on_return=self._reset_on_return, _dispatch=self.dispatch, dialect=self._dialect, ) def dispose(self): while True: try: conn = self._pool.get(False) conn.close() except sqla_queue.Empty: break self._overflow = 0 - self.size() self.logger.info("Pool disposed. %s", self.status()) def status(self): return ( "Pool size: %d Connections in pool: %d " "Current Overflow: %d Current Checked out " "connections: %d" % ( self.size(), self.checkedin(), self.overflow(), self.checkedout(), ) ) def size(self): return self._pool.maxsize def timeout(self): return self._timeout def checkedin(self): return self._pool.qsize() def overflow(self): return self._overflow def checkedout(self): return self._pool.maxsize - self._pool.qsize() + self._overflow class NullPool(Pool): """A Pool which does not pool connections. Instead it literally opens and closes the underlying DB-API connection per each connection open/close. Reconnect-related functions such as ``recycle`` and connection invalidation are not supported by this Pool implementation, since no connections are held persistently. """ def status(self): return "NullPool" def _do_return_conn(self, conn): conn.close() def _do_get(self): return self._create_connection() def recreate(self): self.logger.info("Pool recreating") return self.__class__( self._creator, recycle=self._recycle, echo=self.echo, logging_name=self._orig_logging_name, use_threadlocal=self._use_threadlocal, reset_on_return=self._reset_on_return, pre_ping=self._pre_ping, _dispatch=self.dispatch, dialect=self._dialect, ) def dispose(self): pass class SingletonThreadPool(Pool): """A Pool that maintains one connection per thread. Maintains one connection per each thread, never moving a connection to a thread other than the one which it was created in. .. warning:: the :class:`.SingletonThreadPool` will call ``.close()`` on arbitrary connections that exist beyond the size setting of ``pool_size``, e.g. if more unique **thread identities** than what ``pool_size`` states are used. This cleanup is non-deterministic and not sensitive to whether or not the connections linked to those thread identities are currently in use. :class:`.SingletonThreadPool` may be improved in a future release, however in its current status it is generally used only for test scenarios using a SQLite ``:memory:`` database and is not recommended for production use. Options are the same as those of :class:`_pool.Pool`, as well as: :param pool_size: The number of threads in which to maintain connections at once. Defaults to five. :class:`.SingletonThreadPool` is used by the SQLite dialect automatically when a memory-based database is used. See :ref:`sqlite_toplevel`. """ def __init__(self, creator, pool_size=5, **kw): Pool.__init__(self, creator, **kw) self._conn = threading.local() self._fairy = threading.local() self._all_conns = set() self.size = pool_size def recreate(self): self.logger.info("Pool recreating") return self.__class__( self._creator, pool_size=self.size, recycle=self._recycle, echo=self.echo, pre_ping=self._pre_ping, logging_name=self._orig_logging_name, use_threadlocal=self._use_threadlocal, reset_on_return=self._reset_on_return, _dispatch=self.dispatch, dialect=self._dialect, ) def dispose(self): """Dispose of this pool.""" for conn in self._all_conns: try: conn.close() except Exception: # pysqlite won't even let you close a conn from a thread # that didn't create it pass self._all_conns.clear() def _cleanup(self): while len(self._all_conns) >= self.size: c = self._all_conns.pop() c.close() def status(self): return "SingletonThreadPool id:%d size: %d" % ( id(self), len(self._all_conns), ) def _do_return_conn(self, conn): pass def _do_get(self): try: c = self._conn.current() if c: return c except AttributeError: pass c = self._create_connection() self._conn.current = weakref.ref(c) if len(self._all_conns) >= self.size: self._cleanup() self._all_conns.add(c) return c def connect(self): # vendored from Pool to include use_threadlocal behavior try: rec = self._fairy.current() except AttributeError: pass else: if rec is not None: return rec._checkout_existing() return _ConnectionFairy._checkout(self, self._fairy) def _return_conn(self, record): try: del self._fairy.current except AttributeError: pass self._do_return_conn(record) class StaticPool(Pool): """A Pool of exactly one connection, used for all requests. Reconnect-related functions such as ``recycle`` and connection invalidation (which is also used to support auto-reconnect) are not currently supported by this Pool implementation but may be implemented in a future release. """ @util.memoized_property def _conn(self): return self._creator() @util.memoized_property def connection(self): return _ConnectionRecord(self) def status(self): return "StaticPool" def dispose(self): if "_conn" in self.__dict__: self._conn.close() self._conn = None def recreate(self): self.logger.info("Pool recreating") return self.__class__( creator=self._creator, recycle=self._recycle, use_threadlocal=self._use_threadlocal, reset_on_return=self._reset_on_return, pre_ping=self._pre_ping, echo=self.echo, logging_name=self._orig_logging_name, _dispatch=self.dispatch, dialect=self._dialect, ) def _create_connection(self): return self._conn def _do_return_conn(self, conn): pass def _do_get(self): return self.connection class AssertionPool(Pool): """A :class:`_pool.Pool` that allows at most one checked out connection at any given time. This will raise an exception if more than one connection is checked out at a time. Useful for debugging code that is using more connections than desired. """ def __init__(self, *args, **kw): self._conn = None self._checked_out = False self._store_traceback = kw.pop("store_traceback", True) self._checkout_traceback = None Pool.__init__(self, *args, **kw) def status(self): return "AssertionPool" def _do_return_conn(self, conn): if not self._checked_out: raise AssertionError("connection is not checked out") self._checked_out = False assert conn is self._conn def dispose(self): self._checked_out = False if self._conn: self._conn.close() def recreate(self): self.logger.info("Pool recreating") return self.__class__( self._creator, echo=self.echo, pre_ping=self._pre_ping, recycle=self._recycle, reset_on_return=self._reset_on_return, logging_name=self._orig_logging_name, _dispatch=self.dispatch, dialect=self._dialect, ) def _do_get(self): if self._checked_out: if self._checkout_traceback: suffix = " at:\n%s" % "".join( chop_traceback(self._checkout_traceback) ) else: suffix = "" raise AssertionError("connection is already checked out" + suffix) if not self._conn: self._conn = self._create_connection() self._checked_out = True if self._store_traceback: self._checkout_traceback = traceback.format_stack() return self._conn
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